The present invention relates to an electronic parts mounting apparatus and method which holds an electronic part with a nozzle, and transfers the thus held electronic part to a substrate and mounts the electronic part on the substrate.
In the apparatus for mounting electronic parts on a substrate, a technique for correcting a mounting position of the electronic part by use of an image recognition process is widely used to improve an accuracy of a mounting position of the electronic part on the substrate. In the technique, the transfer head picks up an electronic part from a part supply sections and holds the electronic part with the nozzle, and moves to a substrate along a path. A camera photographs the electronic part held by the head. A photographed image of the electronic part is processed to detect a position shift of the electronic part. When the electronic part is positioned to the substrate, the position shift of the electronic part has been corrected and hence, the electronic part is accurately mounted at its true position.
Techniques for recognizing positions of electronic parts by use of a camera are known. A first technique of them is that the underside of an electronic part is illuminated with light from below, and a camera receives light reflected from the electronic part to photograph an image of the electronic part. The image thus obtained is used for the position recognition. Another technique is a transmission illumination technique. In the technique, a reflecting plate is used which is located on the rearward of an electronic part. Illumination light is projected to the reflecting plate. A camera receives reflecting light from the reflecting plate. An image photographed is used for the position recognition. A further known technique uses two different recognition systems which are respectively applied to their own objects to be recognized, and are selectively used according to an object to be currently recognized. Those systems are installed in one electronic parts mounting apparatus (see for example, JP-A-08-153997<Japanese Patent Application Publication Number: Hei08-153997.>). The electronic parts mounting apparatus currently used includes different light sources. Alight source is selected from those light sources according to a shape, size and surface property of an electronic part to be recognized. Thus, plural recognition systems can selectively be used.
In the electronic parts mounting apparatus of the type in which the plural recognition systems are selectively operated, the mounting position accuracy sometimes varies owing to characteristics of the recognition systems. To be more specific, also when an electronic part being in a same state is photographed by one and the same camera, the result of the position recognition based on an image of the electronic part photographed by the transmission illumination is sometimes different from the result of the position recognition based on an image of the electronic part photographed by the reflection illumination.
This recognition result difference is caused by various factors: for example, the difference between the transmission illumination system in which a silhouette of an outside shape of the electronic part is presented as an image and the reflection illumination system in which a shape of the underside of the electronic part is presented as an image, further, diffraction of the illumination light in the transmission illumination, and others. For this reason, when the part mounting work is performed by properly selecting the recognition system according to an object to be recognized in the electronic parts mounting apparatus of the type in which the plural recognition systems are selectively operated, the position recognition result difference as stated above causes the part mounting accuracy to vary.